(1) Field of the Invention
The present invention relates to methods used to fabricate semiconductor devices, and more specifically to a method used to protect metal interconnect structures, exposed during photoresist stripping procedures.
(2) Description of Prior Art
The use of low dielectric constant materials, such as a hydrogen silsesquioxane, (HSQ), used as interlevel dielectric layers, in semiconductor devices, offers reduced capacitance, and therefore improved device performance, when compared to higher dielectric constant materials, such as silicon oxide. The HSQ layer, featuring a dielectric constant of about 2.8 to 3.0, is sometimes covered with a thin silicon oxide layer, used as a hard mask, offering protection to the HSQ layer during conventional semiconductor fabrication procedures, such as dry etching and photoresist stripping. However when a via hole is formed in the composite insulator layer, comprised of silicon oxide, on HSQ, the sides of the HSQ still remain exposed to subsequent processing, such as a final wet strip, used to remove the defining photoresist pattern. This can result in solvent being trapped in the HSQ layer, with subsequent processing allowing outgassing of the trapped solvent, possibly inducing corrosion of an adjacent aluminum based metal structure, exposed in the newly formed via hole.
In addition to trapped solvents in HSQ layers, resulting from a wet strip of a defining photoresist shape, these same solvents can directly attack, and corrode, exposed aluminum based structures. This is evident when a non-fully landed, or an unlanded via hole, is formed, exposing a portion of an underlying aluminum based structure. An overlying barrier layer, such as titanium nitride, can only protect the top surface of the underlying aluminum based structure, from the wet strip solvents, however offering no protection of the exposed sides of the aluminum based structure, in the unlanded via hole. Therefore the exposed sides of the aluminum based structure, in the unlanded via hole, can be attacked by either outgassing of solvents, from the HSQ layer, during subsequent processing procedures, or attacked directly by these same solvents, during the photoresist wet strip procedure.
This invention will teach a process used to passivate, or protect the exposed surfaces of the aluminum based structure, from the solvents used for the final, wet strip process. The invention features the insertion of a H.sub.2 O/N.sub.2 plasma procedure, between a photoresist dry removal step, and the photoresist wet stripping step. The H.sub.2 O/N.sub.2 plasma treatment results in the growth of an Al.sub.2 O.sub.3 layer, on the exposed sides of the aluminum based structure, as well as forming a passivating layer, on the sides of the exposed HSQ layer, thus resulting in protection of the aluminum based structure, during the photoresist wet strip procedure, as well as during subsequent processing procedures. Prior art, such as Chan et al, in U.S. Pat. No. 5,792,672, describe a H.sub.2 O plasma treatment, followed by a dry strip procedure, used to remove the defining photoresist shape. That prior art however, does not use an initial dry strip, followed by the H.sub.2 O/N.sub.2 plasma treatment, prior to the wet strip, essential when an HSQ surface, as well as an aluminum based surface, is exposed.